An updated taxonomy of the genus Phlogacanthus (Acanthaceae) in Vietnam Author Do, Hai Van Department of Botany, Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam dovanhaiiebr@gmail.com Author Nguyen, Mai Thi Department of Botany, Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam Author Nguyen, Huong Thi Thanh Department of Botany, Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam Author Choudhary, Ritesh Kumar Biodiversity & Palaeobiology Group, Agharkar Research Institute, G. G. Agarkar Road, Pune- 411004, India Author Deng, Yunfei Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China. text Phytotaxa 2018 2018-10-12 372 2 167 175 http://dx.doi.org/10.11646/phytotaxa.372.2.3 journal article 10.11646/phytotaxa.372.2.3 1179-3163 13728728 Phlogacanthus datii (Benoist) D.V.Hai, Y.F.Deng, R.K.Choudhary , comb. nov. ( Figs. 3 & 4 ) Basionym: Cystacanthus datii Benoist (1928: 908) . Lectotype (designated here):— VIETNAM . Lac Tho, 1892, Bon 5301 (P-03578821!; isolectotypes : P-03578822!; P-03578825!). Notes: When Benoist (1927: 908) described this species, he cited two collections in the protologue, i.e. Bon 301 from Tonkin (present day Viet Nam ) and Spire 1508 from Laos , without designating a holotype . A search of these specimens revealed that one specimen of Bon 301 at P (P-03578821) has branches with open flowers, which matches very well with the diagnostic characters of the species mentioned in the protologue, and it is selected here as the lectotype for the name Cystacanthus datii ( Fig. 5 ) according to Art. 9.2, 9.11 & 9.12 of the ICN ( Turland et al. 2018 ). The remaining duplicates are designated here as the isolectotypes . FIGURE 1 . Phlogacanthus paniculatus (T. Anderson) J.B. Imlay : A. Flowering and fruiting twig; B. Calyx and bracteoles; C. Corolla (open); D. Ovary and style; E. Fruit (Open) (Illustration drawn by Mrs Le Kim Chi, from D.V. Hai 14 , HN). Shrubs 1 m tall, erect. Stems subterete or slightly 4-angled, pubescent, soon glabrescent. Petiole 2–2.5 cm ; leaf blade ovate to oblong, 4.5–14 × 2–6 cm , abaxially glabrous and puberulent along veins, adaxially glabrescent, secondary veins ca. 4 on each side of midvein, base cuneate to rounded, margin entire, apex acuminate to acute. Thyrses paniculate, to 15 cm ; bracts linear-lanceolate, 5–8 mm , densely gland-tipped trichomes; bracteoles similar to bracts but smaller. Pedicel ca. 10 mm , gland-tipped trichomes. Calyx ca. 7–10 cm , outside pubescent with gland-tipped trichomes, inside slightly pubescent; lobes linear, 6–9 × 1 mm , equal, apex acute. Corolla pale yellow with thin to dense purplish dots, 2.5–3 cm , ventricose, incurved, outside gland-tipped pubescent; tube basally ca. 2 mm wide and short then wide at middle; usually bent ca. 90º and abruptly inflated near middle; limb 2-lipped; lower lip 3-lobed, lobes ovate and equal; upper lip 2-lobed; lobes ascending cochlear in bud. Stamens 2; filaments ca. 1–1.5 cm , basally pilose; anther thecae oblong, ca. 3–4 mm , connective barbate; staminodes filiform, ca. 1.5–2 mm . Ovary ca. 3–4 mm , oblong, pubescent, with 4 ovules per locule; style ca. 10–12 mm , sparsely pubescent or glabrescent; stigma entire. Capsule clavate, ca. 2.5 cm , pubescent, 8-seeded. Seeds ovate, compressed. FIGURE 2 . Phlogacanthus paniculatus (T. Anderson) J.B. Imlay : A. Flowering and fruiting twig; B. Flower (front view); C. Calyx and flower; D. Calyx and fruit (Photos by D.V. Hai). Distribution: Laos, Vietnam. Habitat : Under evergreen broad-leaved forest, 200 m a.s.l. Phenology : Flowering from March to April. Specimens examined: VIETNAM : Vinh Phuc Province : Phuc Yen town, 15 April 2008 , D.V. Hai 05 (HN); 21°23 ′ 37.1 ″ N , 105°43 ′ 11.6 ″ E , 222 m a.s.l.; 16 March 2014 , D. V . Hai , T . X. Thanh HT 01 ( HN ) ; same locality, 26 April 2004, V.X. Phuong 7592 (HN). Hòa Bình Province : Kim Boi District, Thuong Tien Commune, 23 December 1999 , V.X. Phuong 2537 (HN). Son La Province : Moc Chau District, Muong Sang Commune, 13 April 1977 , H.T. Dung 186 (HN). LAOS : Luang Prabang , Spire1508 (P!).